A producing well will have a wellhead or Christmas tree at the surface for controlling the well. The wellhead assembly supports casing which extends into the well. Tubing extends through the casing for producing the formation fluids. The Christmas tree is a tubular body having a bore extending vertically through it with outlets leading from the bore through the sidewall. Valves are mounted in the bore and to the outlets of the tree for providing access to the tubing as well as directing the produced fluid out to a flow line.
From time to time, many wells require the injection of a treating fluid. One technique know as fracing involves pumping high pressure fluid into the well to fracture the formation to enhance its production. Small hard spheres called proppants are contained in the slurry being pumped into the well. Other techniques involve pumping corrosive fluids such as acid into the well to enhance formation fluid production.
During the well treatment process, lines from large pumps will be connected to the wellhead to pump the treatment fluid through the wellhead and down the tubing. The treatment fluid can be damaging to the interior of the bore of the wellhead. Acids may be corrosive, and slurries with proppants can cause erosion of the wellhead bore. To avoid damage, isolation tools have been used to isolate the bore of the wellhead. A typical isolation tool has a lubricator housing that mounts to the upper end of the wellhead. A tubular mandrel with a piston is located in the housing. After the housing is installed on the wellhead, the operator opens the wellhead master valve and applies hydraulic pressure to the piston to force the mandrel downward. The lower end of the mandrel will extend through the bore of the wellhead and sealingly into the tubing. A treatment line is connected to the upper end of the lubricator housing for delivering the fluid through the mandrel and into the tubing.
While workable, one disadvantage is that the upper end of the lubricator housing can be quite high because the housing has to be at least as long as the mandrel. The mandrel has to be long enough to extend completely through the wellhead into the tubing. Connecting the treatment line to the top of the housing is difficult.
Also, the nozzles located at the lower ends of prior art isolation tools do not adequately protect the production tubing from excessive wear. With high flow rates, the nozzles direct the fluid outward at high velocities which can wear the inside of the tubing, particularly if the injection fluid has solids contained therein.